15 August 2019

Interesting ways plants have adapted

From fire protection to false flowers, we celebrate the many ways plants have adapted over the last 160 million years.

Mark Chase

By Meryl Westlake and Professor Mark W Chase

Orange flowers

When is a flower more than a flower?

Have you ever looked at a single flower to discover it is, in fact, a false flower, one made up of many little flowers?

Plants like daisies have many small flowers (florets) that sit on a central disc surrounded by other flowers that make a single petal.

So, in fact, that typical yellow centre and white petals you see is not just one flower, but lots of them put together in a compound structure called a capitulum. 

Almost all members of Asteraceae, one of the two largest families of flowering plants (the other is the orchid family), have this ‘capitulum’, a single flower head made up of many florets.

This adaptation increases the number of flowers that can be pollinated by one single visit from a pollinator. Other families with similar false flowers include Aristolochiaceae, Araceae and Caprifoliaceae.

White swan (Echinacea purpurea) in the Evolution Garden
White swan (Echinacea purpurea)
An orange Hellenium  in the Evolution Garden
Hellenium, Evolution Garden

Surviving fire

Fire can devastate a landscape, but some plants have adapted to spread when things start heating up.

In the sugarbush family (Proteaceae), some species of Grevillea have adapted to produce fewer seeds and the ones they do produce can withstand the flames.

By spending less energy on making fruits and seeds, they can direct more towards storage organs, like their roots, which gives them the ability to re-sprout after a blaze.

Other related plants, like Persoonia, produce a corky bark that protects buds on their trunks from fire.

These are useful adaptations. As our climate gets more extreme, we should study how these plants have protected themselves and learn from their secrets.  

 

Hakea (Grevillea) in the wild
Hakea (Grevillea) in the wild © Maarten Christenhusz
The Hakea (Grevillea) fruit after a burning
The Hakea (Grevillea) fruit after a burning © Maarten Christenhusz

Helping the bees along

Insect pollination is a vital part of reproduction. 

Plants help pollinators like bees and butterflies drop in and enjoy a meal before moving on and spreading their pollen.

Some adaptations make it easy for as many different pollinators as possible, like the buttercup.

The floral structure of these brightly coloured flowers is simple.

Their shiny petals attract pollinators. Their rosette-like pattern of petals and sepals open around a globe-shaped receptable that, combined with the arrangement of stamens and carpels, guides a pollinator towards the nectar.

An even cleverer adaptation can be seen in the Salvia, from the family Lamiaceae, which has evolved to present a challenging but rewarding opportunity.

The plant has a two-lipped flower and a stamen that acts as a pollen-placing lever.

When a bee enters the flower, the pollen is deposited precisely onto their back, so that when they move to a next flower, it’s in the right place for a smooth transfer.

The plant has evolved so that only certain pollinators with the characteristics to overcome the floral traits can enjoy its goodies, ensuring a loyal customer base with less competition from other animals.

Flowers, Salvia, Kew
Salvia at Kew

Bacteria buddies

Nitrogen fixation is a fascinating process that allows plants use the nitrogen from the atmosphere (in which form it is unusable by plants).

Bacteria located in root nodules convert the nitrogen into something useable (ammonia), from which the plants can produce the amino acids and proteins they need.

In the genus Gunnera, the plants have glands that secrete sugar-rich mucilage (a gooey fluid), and this attracts a photosynthetic bacterium called Nostoc, which fixes nitrogen for its host and in return receives carbohydrates.

Gunnera
Gunnera at Kew Gardens

Ways for water

Plants from different families have developed in similar ways to solve problems.

Kniphofia (Asphodelaceae family) and Yucca (Asparagaceae family) both have leaves arranged like a rosette, which collects water and directs it to their roots.

Other plants in separate families have developed a completely different strategy to minimise water use.

Equisteum (a fern relative) and Ephedra (a gymnosperm) have almost eliminated leaves (reduced to a small ring of tissue) and made their stems the photosynthetic organ so that water loss is minimised and high levels of light are sustained. 

Dutch rush
Dutch rush (equisetum hyemale)

Tasty and useful

Leaves, fruits and seeds are often delicious, and their tastiness makes them targets for hungry animals.

Angiosperms are flower-bearing plants. The edible-quality of their fruits attracts animals to gobble them up…and pass them on, literally.

The bunches of brightly coloured, yummy fruits on a grapevine are prominently displayed so that birds can find and eat them. Cherry fruits are swallowed whole and their single hard stone protects the seed within and passes through the animal, which results in dispersal of the seeds across the landscape. 

Cherry fruits in a tree branch
Cherries ©Macu ic on Unsplash

Chemical warfare

Keeping safe is an instinctive reaction for all life.

Like most plants, legumes are vulnerable to insects, which love their protein-rich seeds and tasty leaves.

Legumes have therefore evolved a set of chemical weapons that protect them by being toxic to animals (including humans).

Unexpectedly, the same chemicals that ward off leaf predators can be used medicinally if we control dosage. Galegine, the chemical used as a model for development of the diabetic drug metformin, comes from goats rue (Galega officinalis), and presence in a pasture of sainfoin (Onobrychis viciifolia) helps to control gut parasites in small livestock.

Chickpeas in the Kitchen Garden
Chickpeas in the Kitchen Garden
Agius Evolution Garden view

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